I am replacing the stock powerglide by a mid seventies th350 in a 67 impala convertible (327). The flexplate was in good condition, no cracks or anything like that, so I left it in place. The torque converter came with the trans and I was told it was a stock converter. With the trans bolted but not torqued to the motor and the converter all the way back in the trans, there is a 5/16 gap between the pads on the converter and the flexplate.
The more I read about it, the more I find that I should shim it with grade 8 washers to reduce the gap. I'm thinking of washers of 1/8in in thickness. When I pull the converter against the flexplate, it's flush with it and it rotates freely with no leak. What do you guys think I should do? leave it alone and bolt it the converter to the flexplate like that or shim it?

Also, I got a Lokar linkage kit with an adjustable bracket, thinking I needed it. It's more of a direct link to the trans as opposed to the stock linkage that has the rod from the column going to a bracket with a pin connected to another spring loaded bracket on the trans. More complicated but perhaps better. Any opinion?

That is normal clearance . Just bolt it up and go. Use the linkage from a '69-'70 t350 car for column shift. Powerglide linkage is different. You can still use the vertical rod from column. I put a t350 into a '66 impala and used the column linkage from a '70 to make it work.

Follow-up: I shimmed the converted to the flexplate with two 1/16 grade 8 washers and 0.75in in length grade 8 bolts from home depot. The 5/16 gap was probably ok but I worried about the fact that all the specs I read said no more than 3/16. I appreciate the answer though.

Linkage is done. PRND lines up. L2 is almost on the L. L1 is further to the right.

I had to redo the double flares on the cooling lines as nuts and fittings were in bad shape. First time doing that. those 5/16 lines are HARD!

I got a holley bracket for the kickdown cable but it's in the way of the stock throttle spring. I think I'll get a bracket for that. The kickdown cable seems to be too long and the ball on the stock qjet carb does not allow to bolt mid way thru the end of the cable. Does anybody know how to solve this?

I still have an issue with the throttle and the kickdown cable. The kickdown cable (from a junkyard from an early elcamino) kindda sticks and does not retract back on its own and make the whole thing stiff). I'll post a youtube tonight to show the situation. Thanks for reading.